Conventionally, there has been known a method of manufacturing a semiconductor device which includes a glass film forming step where a glass film is formed on a surface of a semiconductor wafer by electrophoresis (see patent literature 1, for example). The conventional method of manufacturing a semiconductor device includes, as shown in FIG. 15A to FIG. 15D and FIG. 16A to FIG. 16D, “semiconductor wafer preparing step”, “glass film forming step”, “oxide film removing step”, “roughened surface region forming step”, “electrode forming step”, and “semiconductor wafer cutting step” in this order. Hereinafter, the conventional method of manufacturing a semiconductor device is explained in the order of steps.
(a) Semiconductor Wafer Preparing Step
Firstly, a p+ type diffusion layer 912 is formed by diffusing a p type impurity from one surface of an n− type semiconductor wafer (n− type silicon wafer) 910, and an n+ type diffusion layer 914 is formed by diffusing an n type impurity from the other surface of the n− type semiconductor wafer 910 thus forming a semiconductor wafer having a pn junction parallel to a main surface of the semiconductor wafer. Thereafter, oxide films 916, 918 are formed by thermal oxidation on a surface of the p+ type diffusion layer 912 and a surface of the n+ type diffusion layer 914 respectively (see FIG. 15A).
Next, a predetermined opening portion is formed on the oxide film 916 at a predetermined position by photo etching. After etching the oxide film, subsequently, the semiconductor wafer is etched thus forming a trench 920 having a depth which goes beyond the pn junction as measured from one surface of the semiconductor wafer (see FIG. 15B).
(b) Glass Film Forming Step
Next, a glass film 924 is formed on an inner surface of the trench 920 and a surface of the semiconductor wafer in the vicinity of the trench 920 by electrophoresis, and the glass film 924 is densified by being baked (see FIG. 15C).
In the conventional method of manufacturing a semiconductor device, in forming the glass film 924 by electrophoresis, as shown in FIG. 17, a first electrode plate 14 connected to a minus terminal and a second electrode plate 16 connected to a plus terminal are disposed so as to opposedly face each other in the inside of a tank 10 in which a suspension formed by suspending fine glass particles in a solvent is stored in a state where the first electrode plate 14 and the second electrode plate 16 are immersed in the suspension, and the glass film 924 is formed on a glass film forming scheduled surface (an inner surface of the trench in FIG. 17) by electrophoresis in a state where the semiconductor wafer W is disposed between the first electrode plate 14 and the second electrode plate 16 in a posture where the glass film forming scheduled surface is directed toward a first electrode plate 14 side. As fine glass particles, for example, lead borosilicate glass which contains PbO, B2O3 and SiO2 as main components is used.
(c) Oxide Film Removing Step
Next, a photoresist 926 is formed so as to cover a surface of the glass film 924. Thereafter, the oxide film 916 is etched using the photoresist 926 as a mask so that the oxide film 916 at a portion 930 where a Ni-plating electrode film is to be formed is removed (see FIG. 15D and FIG. 16A).
(d) Roughened Surface Region Forming Step
Next, a surface of the semiconductor wafer at the portion 930 where the Ni-plating electrode film is to be formed is subjected to surface roughening treatment thus forming a roughened surface region 932 for enhancing adhesiveness between a Ni plating electrode and the semiconductor wafer (see FIG. 16B).
(e) Electrode Forming Step
Next, Ni plating is applied to the semiconductor wafer thus forming an anode electrode 934 on the roughened surface region 932 and forming a cathode electrode 936 on the other surface of the semiconductor wafer (see FIG. 16C).
(f) Semiconductor Wafer Cutting Step
Next, the semiconductor wafer is cut by dicing or the like at a center portion of the glass film 924 thus dividing the semiconductor wafer into chips whereby mesa semiconductor devices (pn diodes) are manufactured (see FIG. 16D).
According to the conventional method of manufacturing a semiconductor device, the semiconductor wafer is cut after the glass film 924 is formed in the inside of the trench 920 and hence, highly reliable mesa semiconductor devices can be manufactured.